Multilayer fuser rolls having fluoropolymer coating on a compliant baselayer and method of forming

ABSTRACT

A fuser member for fixing toner to a recording medium having a fluoropolymer non-stick topcoat on a compliant silicone rubber baselayer bonded to a metallic insert is provided. The fluoropolymer is adhered to the silicone rubber baselayer using a primer of a blend of silane and a polyamide resin. The primed silicone baselayer is preheated in an infrared oven to remove low molecular weight fractions. A primer is applied to the prebaked rubber and completely dried before applying the fluoroelastomer topcoat by spraying,

This application is a continuation of Ser. No. 09/012,522 filed Jan. 23,1998.

FIELD OF THE INVENTION

The invention relates to fusing members for use in photocopying andother printing operations which have a non-stick coating on a compliantbaselayer, and more particularly to a multi-layer roll having afluoropolymer coating bonded to a compliant silicone rubber layer on ametallic core.

BACKGROUND OF THE INVENTION

The use of a fusing member constructed with a non-stick material as atop layer and a heat resistant base layer has been known in thereprophotographic art. Typical non-stick materials which have been usedinclude polytetrafluoroethylene (PTFE), fluorinated ethylene propylene(FEP), perfluoroalkoxy (PFA), polychlorotrifluoroethylene (PCTFE),ethylene-chlorotrifluoroethylene (ECTFE), ethylene-tetrafluoroethylene(ETFE), polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF),silicone compounds and blends of these materials.

Fluoropolymer resin by itself, though an excellent non-stick material,provides no compliance. Silicone compounds on the other hand, whilecompliant are readily adversely affected by silicone oil which iscommonly used as a release agent in fusing applications. As the siliconecompound swells, the nip characteristics change, affecting the fusequality of the images. The silicone coating becomes susceptible tomechanical damage, such as abrasion by the print media, picker fingersand hardened toner that accumulates in the system. Fluoroelastomers, onthe other hand are tougher materials which are more resistant tosilicone oil. However, fluoroelastomers generally require a special oilto function in a fuser application. These special silicone oils arecostly and when present on the copy media make writing on the medianoticeably more difficult.

It is preferable to have a material combining the non-stick propertiesof fluoropolymer resins and the compliant properties of siliconeelastomers. U.S. Pat. No. 3,435,500 to Aser and U.S. Pat. No. 4,789,565to Kon disclose applying a polytetrafluoroethylene resin to a siliconerubber surface which is adhered to a metal insert and sintering theresin. Another U.S. Pat. No. 5,547,759, to Chen, et al. discloses amethod of bonding a fluoropolymer resin to various substrates includingsilicone, via a layer of fluoroelastomer and fluoropolymer containing apolyamide-imide layer. The fluoropolymer in the latter case assumes therole of an insulator to prevent degradation of the compliant substrateand the adhesion between the layers during the sintering process.

Since most commercially available materials today compromise onenecessary property in some way or another, the various solutionssuggested in the prior art are not fully satisfactory. This isparticularly true in color systems where gloss and gloss maintenance isa key element of the fusing system. Here, a fluoropolymer coatingpossessing easy wettability by a silicone release agent is a highlydesirable surface characteristic.

Accordingly, it remains highly desirable to provide a fuser member wherethe top layer provides maximum release properties and is not affected bythe use of release agents commonly in use as well as possessingcompliant properties.

SUMMARY OF INVENTION

Generally speaking, in accordance with the invention, a multilayer fuserroll construction having a compliant silicone baselayer bonded to ametallic core and a fluoropolymer coating bonded to the silicone layeris provided. This multilayer roll includes a primer layer of a blend ofsilicone and polyamide resin on the silicone baselayer which ispre-baked in an IR oven prior to disposing a PTFE primer thereon forbonding the fluorocarbon resin coating thereon.

Accordingly, it is an object of the invention to provide an improvedmulti-layer fuser roll having a non-stick coating on a compliant baselayer adhered to a metallic core.

It is a further object of the invention to provide a multi-layer fuserroll having a fluoropolymer coating on a compliant base layer adhered toa metallic core.

It is another object of the invention to provide a multi-layer fuserroll having a fluoropolymer coating on a silicone rubber base coatadhered to a metallic core.

It is yet another object of the present invention to provide a novelprimer composition for bonding a fluoropolymer coating to a compliantbase layer adhered to a metallic core.

It is yet a further object of the invention to provide a method offabricating a multi-layer fuser roll having a non-stick coating and acompliant base layer on a metallic core.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification anddrawings.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others, and thecomposition possessing the features, properties and the relation ofconstituents and the article possessing the features, properties, andthe relation of elements, which are all exemplified in the followingdetailed disclosure, and the scope of the invention will be indicated inthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a schematic cross-sectional view of a fuser roll testassembly; and

FIG. 2 is a schematic cross-sectional view of a fuser roll constructedand arranged in accordance with the invention showing the multilayerconstruction.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A fuser member prepared in accordance with the invention includes ametallic core with a compliant baselayer bonded thereto and a non-stickcoating which is generally not compatible with the compliant baselayer.In the preferred embodiment, the fuser member has an aluminum core, asilicone rubber baselayer and an outer fluoropolymer coating. A primerlayer of a blend of silane and polyamide resin is disposed on thesilicone rubber baselayer which is prebaked in an IR oven prior todisposing the outer fluoropolymer coating thereon. The multi-layer fusermember made in accordance with the invention is fabricated by molding,grinding, pre-heat/sealing, application of top layers, sintering, andfinal polishing.

A fuser roll is fabricated by liquid injection molding a siliconecompound onto an aluminum insert. Prior to the molding process, thealuminum insert is prepared by first cleaning the surface by degreasingand then a silicone rubber primer is applied by spraying. Typicalsilicone rubber primers for adhering to a metallic substrate arevinyltrimethoxysilane, gamma-methacyloxypropyltri-methoxy silane,vinyltris (T-butylperoxy) silane and partially hydrolyzed silanematerials. Commercially available products of these materials include SS4004 & 4155 from GE, DC 1200 & DC 6060 from Dow Corning, 790 fromWacker, Chemlok 608 & 607 and Thixon 5151. Chemlok is a tradename ofLord Corporation & Thixon is a tradename of Morton International Inc.

The injection molding process may be carried out using a 2 cavity moldconnected to a liquid injection machine. The silicone rubber compound isinitially cured in the mold for about 90 seconds at 204° C. (400° F.)and then post cured in an air circulating oven for 1 hour each at 93°C., 121° C., 149° C., 177° C., 204° C. and 232° C. (200° F., 250° F.,300° F., 350° F., 400° F. and 450° F.) Depending on the material andthickness, post curing can also be conducted in a vacuum oven.

The post cured silicone baselayer of each roll is then ground to thedesired finished diameter and roughness. The thickness of the siliconecoating applied can range anywhere from about 0.25 to 10.00 mm, andpreferably between 2 to 7 mm. The surface finish of the ground siliconeshould be no rougher than about 40 Ra.

The ground sample is then subjected to another cleaning process toremove any dust particles on the surface followed by an aqueous washingoperation. The cleaned roll is then sprayed with a primer which is ablend of silane and a polyamide resin. The silane component of the blendcan be made from the same silanes as used to adhere the silicone to themetal substrate. These silanes include vinyltrimethoxysilane,gamma-methacryloxypropytri-methyxysilane, 3-glycidoxyproplytrimethoxysilane. The polyamide resin dispersed therein is preferably selectedfrom the group comprising Versamid 100, Micromid 632 HPL, Micromid 141L,Versamid 100X65 and Versamid 100T60. Versamid and Micromid aretrademarks of Henkel Corporation and Union Camp Corporation,respectively.

An important step in the process of fabricating the multi-layer roll inaccordance with the invention is a pre-baking operation prior todeposition of the non-stick coating. The preferred silicone compoundbaselayer used are those based on addition cured systems where noreaction by-product is generated during the curing cycle. However, sincemost silicone compounds contain minor amounts of low molecular weightcyclic fractions, the pre-bake step of the process removes any lowmolecular weight fraction while at the same time transforming the primerlayer into an oxidized state. This renders the surface easily wettableby the top layer primer and making it susceptible to receive the oplayer chemistry.

The IR oven used to pre-bake the primed silicone rubber is about 4.7meters (12 feet) long. The oven speed can be varied from about 20 mm perminute (mm/m) (8 inches per minute (ipm)) to 59 mm/m (22 ipm). The IRoven is capable of heating the roll surface from room temperature toabout 425° C. (800° F.) in about 10 to 12 minutes.

In the pre-baking step, the roll is heated during the initial 2 meters(8 feet) of travel through the oven to about 260° C. (500° F.). The rollis then permitted to dwell at that temperature for the remaining 1.3meter (4 feet) of travel through the oven.

It has been found that if the roll during the pre-baking step isunderbaked, gas is entrapped in the silicone base layer. This preventsadequate bonding of the fluoroelastomer topcoat. If the roll isoverbaked, there is the potential of damage to the primer layer anddamage to the silicone layer.

After the pre-baking step, the roll is allowed to cool. At this time, afinal primer is applied prior to application of the fluoropolymercoating. The final primer is one usually used to adherepolytetrafluoroethylene coatings as suggested by the manufacturer. Suchprimers usually contain PTFE and fluorinated ethylene propylene resinwith polyamide or polyamide-imide polymers. A preferred primer includesthe polyamide-imide polymer.

The fluoropolymer material for the coating is applied to the primedprebaked silicone rubber surface of the roll using spray equipment intwo steps. There is a mid-coat and a top-coat as suggested by themanufacturer. The roll is weighed and the coating is applied to generatea final coating thickness of about 2.5 to 6.5 micron (0.7-1.6 mils)coating thickness. The coated roll is then re-weighed. For each type ofroll, there is a weight target for each coating layer. The topcoatprimer layer must be completely dry before the mid and topcoat layersare applied. The midcoat must be wet when the topcoat is applied.

After spraying, the liquid-coated roll is cured using an infrared oven.The upper limit of the cure temperature is determined by the temperatureat which the silicone rubber and/or primer layer begins to break down.Though experimentation, this temperature has been determined though itis variable depending on the construction of the roll. For thickerwalled rolls the maximum temperature is about 393° C. (740° F.). Forthinner walled rolls the maximum temperature is about 371° C. (700° F.).There are several indications of an overcured roll so that this can bemonitored during the processing. The most prominent indication is thecolor of the cured material.

Rolls prepared in accordance with the invention have been cured at boththe maximum and minimum rates through the oven. Based on the foregoingrates, the maximum IR oven time exposure is about 18 minutes. The rollitself does not get above about 204° C. (400° F.) in the first third ofthe oven. Therefore, the maximum time these rolls are in the IR ovenabove the temperature where silicone rubber degrades is about 12minutes. On the other hand, the minimum time is about 4 minutes. Both ofthese exposure times are considered acceptable.

After completion of the cure, the roll is polished using asuperfinishing process, then inspected and packaged. The superfinishingprocess is presently used throughout the industry as a polishingprocess, and is well known to those skilled in the art. The cured andcoated fuser roll is then ready for testing in a test apparatus as shownin FIG. 1.

A fuser roll test assembly 100 is shown generally in FIG. 1 and appliesheat and pressure to fuse a quantity of toner particles 12 on a sheet ofpaper 13 between a fuser roll 20 and a pressure roll 30. Fuser roll testassembly 100 also includes a release agent application unit 11 includinga wick 15 for applying release agent to the surface of fuser roll 20. Astripper finger 16 facilitates the separation of paper 13 from roll 20as it travels in the direction of arrow A.

In FIG. 2, a fuser roll 101 constructed and arranged in accordance withthe invention is shown. Fuser roll 101 includes a solid or hollow coreor insert 102 covered with a baselayer 102 having a primer layer 104disposed thereon and a topcoat 106 disposed on primer layer 103.Baselayer 102 is preferably 0.5 to 5 mil thick and the overall coating(either surface layer 104 or combined layers 102, 103 and 104) should beabout 0.1 to 0.3 microns (3-8 mils) thick.

The following Examples describe the multi-layer fuser rolls havingfluoroelastomer topcoats on a silicone baselayer prepared in accordancewith the invention. These examples are presented for purposes ofillustration only, and are not intended to be construed in a limitingsense.

EXAMPLES 1-6

Tables I and II provide a summary of the results obtained using variouscombinations of components coming within the scope of the invention.Table I shows the results using different PTFE primers and topcoatcompositions on the silicone rubber baselayer.

TABLE I Coating * ** *** Number Primer Midcoat Topcoat ConductiveComments 1 Conductive PFA/PTFE PFA/PTFE Yes First tested technologyPrimer-A Conductive Conductive Mid Coat-A Top Coat-A 2 ConductivePFA/PTFE Yes Mainline development Primer-B Conductive difficult topolish Top Coat-B 3 Non- PFA/PTFE PFA/PTFE No Second mainline ConductiveNon- Non- development. Visual Primer-C Conductive Conductive problemswith roller during Mid Coat-C Top Coat-C life testing. 4 Non- PFA/PTFEPFA No Alternative to #3 difficult Conductive Non- Non- to polish.Primer-C Conductive Conductive Mid Coat-C Top Coat-D 5 Non- PFA/PTFEPFA/PTFE No Current development reduced Conductive Non- Non- toproduction coating. Primer-C Conductive Conductive Mid Coat-D TopCoat-C * Primer Designation Polymer Ingredients A DuPont 855-023 PTFE,FEP Resin, Polyamide Polymer B DuPont 855-024 PTFE, FEP Resin,Polyamide-imide polymer PFA Resin C DuPont 855-021 PTFE, FEP Resin,Polyamide-imide polymer ** Mid Coat Designation Polymer Ingredients ADuPont 855-421 PTFE, PFE-PFAVE Polymer, Acrylic polymer C DuPont 855-401PTFE, Acrylic Polymer D DuPont 855-403 PTFE, FFA Resin, Acrylic Polymer*** Top Coat Designation Polymer Ingredients A DuPont 855-103 PTFE,Acrylic Polymer B DuPont 855-107 PFE-PFAVE Polymer, TFE/PFVE C DuPont855-500 PTFE, Acrylic Polymer D DuPont 855-210 PTFE

Table II sets forth the results demonstrating the improved bondinglevels between the fluoroelastomer coating and the silicone rubberbaselayer in accordance with the invention. Run 1 utilizes a Vistamerhigh density polyethylene from Composite Particles, Inc. dispersed in aThixon silane often used as a silicone rubberprimner material. The bondlevel of 0-2 is poor and not acceptable. A bond level of 8-10 is fullyacceptable.

TABLE II 1 2 3 4 5 6 Thixon 300/301 100.0 X X X X X Chemlok 5151 X 100.0X 50.0 100.0 50.0 Chemlok 607 X X 100.0 50.0 X 50.0 Vistamer HDPE  10.0X X X X X Micromid 632 HDL X  8.0 X  8.0 X X Versamid 100 X X  8.0 X 8.0  8.0 Bond Level 0-2 8-10 4-5 6-8 8-10 6-8 0 - Poor Bond 10 -Excellent Bond

A marginally acceptable bond level of 4-5 is obtained when Versamid 100is dispersed in Chemlock 607. Similar but somewhat better results areobtained when Versamid 100 or Micromid 632 HDL are dispersed in mixturesof Chemlock 5151 and Chemlock 607. The most acceptable and highest bondlevels are achieved when the Micromid or Versamid are dispersed inChemlock 5151.

The improved bond level between the fluoropolymer coating and thesilicone rubber baselayer is evidenced by the performance of rollsprepared in accordance with the invention. It is characteristic of suchrolls not to delaminate during failure. Typically, a line forms at thepicker finger which will indicate a deterioration in copy quality, butthe copier will still make copies. This is due to the higher peelstrength of the fluoroelastomer topcoat utilizing the unique primersystems in accordance with the invention.

Peel strength is defined as the force required to remove thefluoropolymer coating from the silicone baselayer. The test measures theforce in grams necessary to remove a 10 mm wide strip which is pulled ata 90° angle to the part at a rate of 200 mm/min.

The peel strength for typical original equipment manufactured parts isbetween about 20-50 grams. In contrast, in the multi-layer rollsprepared in accordance with the invention the typical peel strength isbetween about 100-250 grams. It is noted that this is a significantmeasurement since the coating for OEM parts typically fail by peelingoff in sheets. This potentially causes the copiers to stop once thepaper paths become plugged with strips of coating. As noted above, themultilayer rolls prepared in accordance with the invention typicallyshow wear in specific areas, but generally do not peel off in sheets dueto the significantly higher peel strength obtained by the invention.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in carrying out the above method, andin the composition and article set forth without departing from thespirit and scope of the invention, it is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Particularly it is to be understood that in said claims, ingredients orcompounds recited in the singular are intended to include compatiblemixtures of such ingredients wherever the sense permits.

What is claimed is:
 1. A method of forming a fuser member, comprising:providing a substrate; depositing a silicone rubber primer on thesubstrate; placing the primed substrate into an injection moldingmachine; injecting a silicone rubber compound about the primed substrateto form a baselayer; curing the silicone rubber baselayer; cleaning thesilicone rubber baselayer; applying a primer of a blend of silane andpolyamide resin that adheres to the silicone rubber baselayer;pre-baking the silicone rubber baselayer; applying a fluoropolymerprimer that adheres to the pre-baked silicone baselayer; spraying afluoropolymer topcoat onto the primed and pre-baked silicone rubbersurface; and curing the coated substrate.
 2. The method of forming afuser member of claim 1, wherein the pre-baking is carried out in aninfrared oven.
 3. The method of forming a fuser member of claim 2,wherein the infrared oven is an elongated apparatus and the fuser memberis transported through the oven at a controlled rate of speed.
 4. Themethod of forming a fuser member of claim 3, wherein the silicone rubbercoated substrate is heated to about 260° C. (500° F.).
 5. The method offorming a fuser member of claim 4, wherein the pre-baked silicone rubbercoated substrate is cooled prior to application of fluoroelastomerprimer.
 6. The method of forming a fuser member of claim 1, wherein thefluoropolymercoating is cured in an infrared oven.
 7. A fuser member,comprising: a substrate; a silicone rubber primer layer disposed on thesubstrate; a silicone rubber baselayer disposed on the primer layer; apre-baked silane and polyamide primer layer disposed on the siliconerubber baselayer; a fluoropolymer primer layer disposed on the pre-bakedand primed silicone baselayer; and a top coat of a fluoropolymerdisposed on the silicone baselayer.
 8. The fuser member of claim 7,wherein the substrate is a metallic substrate.
 9. The fuser member ofclaim 7, wherein the substrate is a metallic roll.
 10. The fuser memberof claim 7, wherein the fluoropolymer coating includes a fluoroelastomermidcoat of polytetrafluoroethylene and a top coat ofpolytetrafluoroethylene and perfluoroalkoxy having a major proportion ofpolytetrafluoroethylene perfluoroalkoxy.
 11. The fuser member of claim10, wherein the fluoropolymer mid coat includes between about 30 to 70weight percent polytetrafluoroethylene and the top coat includes atleast about 70 weight percent polytetrafluoroethylene.
 12. The fusermember of claim 11, further including a polytetrafluoropolymer primerdeposited on the pre-baked silane and polyamide prime layer.
 13. Thefuser member of claim 12, wherein the fluoropolymer mid coat includesabout 50 weight percent polytetrafluoroethylene and 50 weight percentperfluoroalkoxy and the top coat includes about 90 weight percentpolytetrafluoroethylene and 10 weight percent polytetrafluoroethylene.14. The fuser member of claim 13, wherein the polytetrafluoroethyleneprimer is an aqueous based suspension of polytetrafluoroethylene,fluorinated ethylene propylene resin and polyamide-imide polymer. 15.The fuser member of claim 7, wherein the fluoropolymer primer layerdisposed on the pre-baked primed silicone baselayer is a polyamide-imidefluoropolymer primer.
 16. The fuser member of claim 15, wherein thefluoropolymer coating includes a fluoropolymer midcoat ofpolytetrafluoroethylene and perfluoroalkoxy and a top coat ofpolytetrafluoroethylene and perfluoroalkoxy having a major proportion ofpolytetrafluoroethylene.